This invention relates to a process for reacting maleic anhydride with optionally nuclear-substituted vinylbenzenes to form tetralin dianhydrides at an elevated temperature in the presence of a solvent and hydroquinone while pasing an oxygen-containing nitrogen stream through the reaction mixture. Tetralin dianhydrides are used for the preparation of polyimides, plasticizers for pvc or crosslinking agents for lacquers.
The reaction of maleic anhydride with vinylbenzenes to such dianhydrides has been known for a long time. In order to avoid polymerization, the process is carried out while passing an oxidizing gas through the reaction mixture. Nitrogen having a maximum oxygen proportion of 5% (U.S. Pat. No. 3,769,304) has, inter alia, been disclosed for this purpose. Although there is no explicit statement why the oxygen proportion must not be higher, a possible explanation exists in the remark that the gasous stream must not be flammable.
On the other hand, it has been known from J. Am. Chem. Soc. 78:1017 (1956) and/or 80:2465 (1958) that, with higher oxygen contents in the gaseous atmosphere, styrene is oxidized to styrene oxide or peroxide.